1. Field of the Invention
The present invention relates to a novel process for preparing pyrazolo[5,1-b]quinazolones by reacting isatoic anhydrides with pyrazolones in an inert organic solvent at from 100.degree. C. to 180.degree. C. with simultaneous azeotropic removal of the water formed in the course of the reaction.
2. Discussion of the Background
It is known to prepare 2-methylpyrazolo[5,1-b]quinazolone by reacting isatoic anhydride with 3-methyl-pyrazol-5-one in the melt or in a high-boiling solvent at from 200.degree. C. to 250.degree. C. (Angew. Chem. 74 (1962), 839).
J. Heterocycl. Chem. 18 (1981), 117 and J. Med. Chem. 24 (1981), 735 disclose the preparation of further pyrazolo[5,1-b]quinazolones. The starting materials used are likewise isatoic anhydrides and pyrazolones. This reaction takes place in N,N-dimethylformamide as solvent in the presence of sodium hydride as base at from -10.degree. C. to 0.degree. C.
Neither procedure is easy to carry out on an industrial scale. On the one hand, special measures are required in order to be able to perform the reaction at a very high temperature in a melt or in a high-boiling solvent; on the other hand, the use of sodium hydride as a base is not without its problems and necessitates a great deal of attention to safety.